1. Field of the Invention
The present invention relates generally to truck mounted hydraulically lifted platforms and cargo bodies and, more particularly, to a compound linkage cargo body high-lift mechanism employing a leverage assisting booster arm assembly biased into an upright position by a pair of torsion springs, the mechanism being used to elevate the cargo body to a degree whereby the cargo may be directly transferred to a receiving storage facility or off-loaded for use at an elevated location.
2. Description of the Prior Art
High-lift mechanisms attached to truck chassis are known in the art. Exemplary of these mechanisms is the High-Lift Mechanism disclosed in U.S. Pat. No. 3,891,108, issued to Charles Traficant on Jun. 24, 1976. Traficant teaches the use of a High-Lift Mechanism which uses one or more hydraulic cylinders to lift a cargo body to its upper position. The pair of hydraulic cylinders has a lifting roller assembly on their end. A booster arm is pivotally attached to the lower frame of the mechanism, and is used to engage the axle of the roller assembly at the beginning of the lifting cycle to impart leverage to the lifting cylinders, which is needed to overcome friction forces in the mechanism due to the orientation of the cylinders when the mechanism is in its lowered position relative to the direction of movement of the frame levers of the mechanism. A spring loaded piston assembly is attached to the booster arm to maintain same in a predetermined position when the upper frame is elevated. However, if the spring loaded piston assembly fails or breaks, which frequently occurs through normal wear or through handling of the mechanism in connecting it to a truck chassis, the booster arm is rendered inoperable, which in turn renders inoperable the mechanism.
3. "State of the Art"
U.S. Pat. No. 2,412,158 to N. V. Kuehlman et al. discloses a scissors type of high lift truck mechanism which is directed primarily to providing auxiliary wheels on the freight body to permit the truck proper, that is, the frame and cab, to be withdrawn from the freight body. The scissors type of levers employed are pivotally connected to one end of each lever to eliminate the need for rollers in top and bottom tracks. A portion of the mechanism of this device extends below the truck chassis and the piston head is pivotally connected to the lever mechanism to function as a straight push-type through the entire lift cycle.
U.S. Pat. No. 2,935,218 to C. M. Fritz also discloses a scissors type of high lift truck mechanism which includes pivotally connected levers and a hydraulic cylinder, mounted well below the chassis, which provides a straight push system.
Another type of scissors type of elevating device is disclosed in U.S. Pat. No. 2,945,551 to M. H. Annin et al. Three sets of hydraulic power devices are employed, one pushes vertically, directly on the scissors , the second is longitudinally disposed in the chassis frame and the third is similarly disposed in the elevator platform. The second and third hydraulic devices exert longitudinally directed forces on the ends of the top and bottom scissors levers.
U.S. Pat. No. 3,220,585 to D. N. McCartney et al discloses a high lift trailer employing scissors type of levers, pivotally connected intermediate their lengths. Six hydraulic rams are utilized to lift the load carrying bed. Four small rams are positioned adjacent the four corners of the device to initiate the lifting operation and two large rams are utilized to complete the lift cycle.